1. Field of the Invention
The present invention relates generally to an air suction device for a multicylinder engine, and more particularly, to such an air suction device operative to effect a resonance supercharging in suction stroke of each of cylinders provided in a multicylinder engine and in result to improve air charge efficiency in the cylinders.
2. Description of the Prior Art
In a suction system provided for a multicylinder engine, an intake pressure vibration arises in an inlet passage in response to opening operations of inlet valves disposed in the inlet passage with a specific frequency which is determined in accordance with the configuration of the inlet passage. In connection with this fact, there has been previously proposed a method of charging air into cylinders provided in the multicylinder engine in which resonance supercharging is effected by making good use of the intake pressure vibration and thereby air is effectively charged into the respective cylinders, so that air charge efficiency in each of the cylinders is increased and the output torque characteristic of the engine is improved.
In an air suction device for a multicylinder engine to which the above mentioned method is applied, it is required for improving effectively air charge efficiency in each cylinder to cause the opening operation of each inlet valve disposed in an inlet passage to be performed in synchronism with the period of intake pressure vibration arising in the inlet passage. However, the size and configuration of the inlet passage is ordinarily fixed to be unchangeable, and this results in that usually the air charge efficiency in each cylinder is so restricted as to be improved effectively only when the engine is working at a selected speed within a relatively narrow range of speed extending around a specific speed at which the opening operation of each inlet valve is performed in synchronism with the period of the intake pressure vibration.
For the purpose of solving this problem, there has been also proposed an improved air suction device for a multicylinder engine, as disclosed in, for example, the Japanese patent application published before examination under publication number 56-115818. In the air suction device thus proposed, a surge chamber which is separated off by a partition-wall into two compartments for air expansion is provided in an inlet passage together with a first group of connecting air passages each coupling a corresponding one of a first group of cylinders operative to work with their respective suction strokes which are not successive to one another with one of the compartments and a second group of connecting air passages each coupling a corresponding one of a second group of cylinders operative to work with their respective suction strokes which are not successive to one another with the other of the compartments. The partition-wall in the surge chamber is provided with an opening for connecting the separated compartments with each other and a closing valve for shutting selectively the opening.
With this configuration, the closing valve is controlled in response to the operating condition of the engine, for example, so as to be closed when the engine speed is lower than a predetermined value and opened when the engine speed is equal to or higher than the predetermined value. As a result of such a control of the closing valve, it can be arranged that the opening operation of each inlet valve disposed in the inlet passage is performed in synchronism with the period of intake pressure vibration arising in the inlet passage at both the engine speed lower than the predetermined value and the engine speed higher than the predetermined value. In such a case, resonance supercharging is effected in a wide speed range of the engine and thereby air is effectively charged into the respective cylinders, so that air charge efficiency in each of the cylinders is increased.
In such an improved air suction device proposed previously, however, there are problems that installation of the closing valve at a portion of the partition-wall where the opening is provided in the surge chamber requires a relatively complicated construction for securing the closing valve on the partition-wall and requires also annoying handwork for mounting the closing valve on the partition-wall. Moreover, the surge chamber is apt to be increased in size for reducing difficulties in mounting the closing valve on the partition-wall therein, and this may result in a further problem that the whole device is increased in size.
Further, in the case where the opening provided on the partition-wall and the closing valve installed on the partition-wall for shutting the opening selectively are located at respective inappropriate positions in the surge chamber, intake air flowing through the inlet passage is impeded by the closing valve to be supplied smoothly to the cylinders and therefore the air charge efficiency in each cylinder is not improved. To avoid such a case, both the opening and the closing valve on the partition-wall must be precisely disposed at respective proper positions in the surge chamnber.